Communication Using Function Blocks
6-18
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
6.5
Programming the Function Blocks
This section is intended for all those who have changed from SIMATIC S5 to
SIMATIC S7. The following sections tell you what to watch for when you program
function blocks in STEP 7.
6.5.1
General Information on Data Block Assignment
Addressing
Data operands are addressed in data blocks byte by byte in STEP 7 (instead of
word by word as in STEP 5). You therefore have to convert the addresses of the
data operands.
STEP
5
STEP
7
DW [n]
DL [n]
DR [n]
15 14
13 12 11 10
9
8
7
6
5
4
3
2
1
0
DBW [2n]
DBB [2n]
DBB [2n+1]
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
Figure 6-4
Comparing Data Addressing in STEP 5 and STEP 7
The address of a data word in STEP 7 is doubled compared to STEP 5. It is no
longer divided into a right and a left data byte. Bit numbering is always from 0 to 7.
